1. Field of the Invention
The present invention relates to a liquid ejection head that ejects a liquid to a print medium for printing, and a printing apparatus using the liquid ejection head.
2. Description of the Related Art
In recent years, many printing apparatuses have been used, and for the printing apparatuses, there has been a demand for an increase in printing speed and resolution, an improvement in image quality, and a reduction in noise. An ink jet printing apparatus meets this demand. The ink jet printing apparatus is configured to eject ink droplets through ejection ports formed in a print head as a liquid ejection head to attach the ink droplets to a print medium for printing.
Some ink jet printing apparatuses commonly used adopt a method of ejecting ink droplets using electrothermal transducing elements (heating elements) such as heaters as ejection energy generating elements to eject ink droplets. The method uses the ejection energy generating elements to generate bubbles in ink so that the resulting bubbling pressure allows the ink droplets to be ejected. That is, a voltage is applied to the electrothermal transducing elements to instantaneously boil the ink in the vicinity of the electrothermal transducing elements. Then, the phase-change of the ink occurs to rapidly generate a bubbling pressure to eject the ink droplets at a high speed. This method enables the ejection of the ink droplets to be precisely controlled using electric signals. As a result, an ink jet printing apparatus can be provided which can accurately eject the ink droplets. Furthermore, advantageously, the ink ejecting method using the electrothermal transducing elements, for example, eliminates the need for a large space in which the ejection energy generating elements are disposed, simplifies the structure of the print head, and facilitates integration of nozzles. Therefore, the use of such an ink jet printing apparatus enables letters, images, and the like to be densely printed with a high definition.
Some print heads for the above-described ink jet printing apparatuses are of a type in which a plurality of ink channels communicate with one bubbling chamber as an energy acting chamber as disclosed in U.S. Pat. No. 6,660,175 and Japanese Patent Application Laid-Open No. S58-8658 (1983). In these print heads, two symmetric ink flows flow into an area on each heating element through respective ink channels communicating with the space on the heating element. Then, the heating element is driven to generate bubbles in the ink on the heating element to allow the ink to be ejected through the ejection ports.
However, in the print head ejecting the ink by generating the bubbles, cavitation may occur during debubbling inside the print head. The cavitation rapidly varies the pressure inside the bubbling chamber, which can damage the electrothermal transducing elements. In particular, when such a rapid, repeated pressure variation concentrates at one fixed position inside the ink stored in the print head, a repeated impact is applied to surroundings of the position. This may damage a part of the wall surfaces inside the print head or some of the electrothermal transducing elements. For example, when the rapid pressure variation causes a repeated impact to the electrothermal transducing elements, surfaces of the electrothermal transducing elements may be scraped. Furthermore, depending on the position of the cavitation, wires through which electricity is transmitted may be broken, thereby preventing the electrothermal transducing elements from being driven.